EUI 6.10.5 backport

[chandlerprall]

Creating an issue to track this backport as it's getting large.

• 5 PRs getting backported to 6.10.5 @chandlerprall
  • Allow keyboard navigation of single select combobox #1619 to fix [Security] Uncaught TypeError: Cannot read property 'position' of null error during role creation kibana#33053
  • Adds side nav toggle #1701 for the side nav
  • Fix time selection in EuiSuperDatePicker #1704 for the time selection issue
  • [EuiSuperDatePicker] “Now” tab titled “Set to Now” #1620 for the set to now problem
  • Dark mode redux, fix dark mode docs #1691 for better dark mode
  • One more PRs around nav changes for Kibana
    • Allow EuiListGroupItem to pass a custom element as the icon #1726 for list group item custom icon
    • EuiNavDrawerGroup default icon #1729 for default icon to be provided
• Apply that backport to Kibana 6.7 @chandlerprall
• Backports in Kibana for dark mode changes, nav changes to K 7.0 but not K 6.7. @snide

[snide]

7.0 backport is up elastic/kibana#33273

[chandlerprall]

6.7 backport is merged elastic/kibana#33267